Metal ingots, billets and other castparts may be formed by a casting process which utilizes a vertically oriented mold situated above a large casting pit beneath the floor level of the metal casting facility, although this invention may also be utilized in horizontal molds. The lower component of the vertical casting mold is a starting block. When the casting process begins, the starting blocks are in their upward-most position and in the molds. As molten metal is poured into the mold bore or cavity and cooled (typically by water), the starting block is slowly lowered at a pre-determined rate by a hydraulic cylinder or other device. As the starting block is lowered, solidified metal or aluminum emerges from the bottom of the mold and ingots, rounds or billets of various geometries are formed, which may also be referred to herein as castparts.
While the invention applies to the casting of metals in general, including without limitation, aluminum, brass, lead, zinc, magnesium, copper, steel, etc., the examples given and preferred embodiment disclosed may be directed to aluminum, and therefore the term aluminum or molten metal may be used throughout for consistency even though the invention applies more generally to metals.
While there are numerous ways to achieve and configure a vertical casting arrangement, FIG. 1 illustrates one example. In FIG. 1, the vertical casting of aluminum generally occurs beneath the elevation level of the factory floor in a casting pit. Directly beneath the casting pit floor 101a is a caisson 103, in which the hydraulic cylinder barrel 102 for the hydraulic cylinder is placed.
As shown in FIG. 1, the components of the lower portion of a typical vertical aluminum casting apparatus, shown within a casting pit 101 and a caisson 103, are a hydraulic cylinder barrel 102, a ram 106, a mounting base housing 105, a platen 107 and a base with starting heads 108 (also referred to as a starting block base), all shown at elevations below the casting facility floor 104.
The mounting base housing 105 is mounted to the floor 101a of the casting pit 101, below which is the caisson 103. The caisson 103 is defined by its side walls 103b and its floor 103a. 
A typical mold table assembly 110 is also shown in FIG. 1, which can be tilted as shown by hydraulic cylinder 111 pushing mold table tilt arm 110a such that it pivots about point 112 and thereby raises and rotates the main casting frame assembly, as shown in FIG. 1. There are also mold table carriages which allow the mold table assemblies to be moved to and from the casting position above the casting pit.
FIG. 1 further shows the platen 107 and starting block base 108 partially descended into the casting pit 101 with castpart 113 (which may be an ingot or a billet) being partially formed. Castpart 113 is on the starting block base 108, which may include a starting head or bottom block, which usually (but not always) sits on the starting block base 108, all of which is known in the art and need not therefore be shown or described in greater detail. While the term starting block base is used for item 108, it should be noted that the terms bottom block base and starting head base are also used in the industry to refer to item 108.
While the starting block base 108 in FIG. 1 only shows one starting block 108 and pedestal, there are typically several starting blocks mounted on each starting block base, which simultaneously cast billets or ingots, as the starting block base is lowered during the casting process.
When hydraulic fluid is introduced into the hydraulic cylinder at sufficient pressure, the ram 106, and consequently the starting block base 108, are raised to the desired start elevation for the casting process, which is when the starting blocks are within the mold table assembly 110.
The lowering of the starting block base 108 is accomplished by metering the hydraulic fluid from the cylinder at a pre-determined rate, thereby lowering the ram 106 and consequently the starting block base at a pre-determined and controlled rate. The mold is controllably cooled during the process to assist in the solidification of the emerging ingots or billets, typically using water cooling means. Although the use of a hydraulic cylinder is referred to herein, it will be appreciated by those of ordinary skill in the art that there are other mechanisms and ways which may be utilized to lower the platen.
There are numerous mold and casting technologies that fit into mold tables, and no one in particular is required to practice the various embodiments of this invention, since they are known by those of ordinary skill in the art.
The upper side of the typical mold table operatively connects to, or interacts with, the metal distribution system. The typical mold table also operatively connects to the molds which it houses.
When metal is cast using a continuous cast vertical mold, the molten metal is cooled in the mold and continuously emerges from the lower end of the mold as the starting block base is lowered. The emerging billet, ingot or other configuration is intended to be sufficiently solidified such that it maintains its desired profile, In some casting technologies, there may be an air gap between the emerging solidified metal and the permeable ring wall, while in others there may be direct contact. Below that, there is also a mold air cavity between the emerging solidified metal and the lower portion of the mold and related equipment.
Once casting is complete, the castparts, are removed from the bottom block or starting head.
The casting process is initiated by the introduction of molten metal into the mold cavity and the solidification of the molten metal through the mold cavity occurs by the application of a cooling fluid such as water. The cooling fluid is applied around the perimeter of the mold cavity and in the process, causes the walls of the mold cavity to cool. As the mold cavity wall is cooled the molten metal adjacent to the wall generally solidifies and shrinkage occurs around the solidifying surface of the castpart. The shrinkage of the castpart then causes the solidifying castpart to shrink back away from the cooler mold wall, resulting in some re-melting of solidifying surface of the castpart and expansion back to the mold wall. This solidification process occurs and the resulting castpart emerges out of the mold cavity with a solidified outer surface or skin and the inner core of the castpart is still in its molten state. A continuous supply of cooling fluid is applied to the perimeter of the solidifying castpart emerging from the mold cavity.
At or above the entrance or inlet to the mold, molten metal is delivered by the trough distribution system and provided at a location above the mold inlet. It is generally desirable to monitor, control and maintain the molten metal entering the mold cavity to control the quality and safety of the cast. This may require or include a molten metal surface level sensor which senses the exact surface level of the molten metal to optimize its position relative to the mold.
During the molding process for aluminum and various alloys, certain oxides form on the exposed surface of the molten metal during the casting process. It is undesirable to have oxides form on certain primary areas of the exterior surface of the castpart as it can initiate cracking in the castpart or affect the quality of the castpart for downstream manufacturing and rolling operations on that castpart. For example, larger castparts referred to as ingots would be generally rectangular in shape and would have two larger flat surfaces which would be referred to as the rolling surfaces. When a large ingot is rolled, the rolling surfaces are placed to interface with and between large rollers and through repetitious rolling operations a relatively thick ingot is reduced down to a thickness which may for example be used to manufacture aluminum cans.
It is very desirable in producing castparts destined for certain operations such as rolling, that the oxides be minimized or eliminated on certain critical surfaces of the castpart, such as the rolling surfaces. For an ingot destined to be rolled, it is acceptable to have some level of oxides on the end portions of the cross-section of the ingot because those oxides do not have the as much impact on the rolling surface casting cracking or downstream rolling operations. However, if the oxides are allowed to travel to the rolling surface, the castpart quality will be negatively affected.
This has been a well-known problem in the industry for a long time, and in order to prevent the oxides on the surface of the molten metal from traveling to the rolling surfaces or other surfaces where it is important to minimize the oxides, typical prior art devices utilize what are referred to as dams or oxide barriers. These dams or oxide barriers are generally rectangular, elliptical or circular shaped rings which present a barrier that starts below the surface of the molten metal and extends upward above the surface so that the oxides that are forming on the surface cannot travel or flow to a surface of the castpart. In prior art dams, the oxides buildup relatively quickly within the interior of the dams or oxide barriers and thereby create an elevated surface above the actual molten metal level.
While the dams or oxide barriers do reduce or prevent oxide from traveling or flowing to the protected surfaces they build up oxides within the dam or barrier, the molten metal level sensor detects the varying oxide level above the true molten metal level and is not then able to maintain the molten metal surface at the desired or necessary level relative to the mold to optimize the casting. If for example, the oxide buildup is two to four millimeters above the surface of the molten metal the sensor control system consequently maintains the molten metal level two to four millimeters below its intended location. Unintended and negative consequences may occur. These consequences may include lower quality casting or a condition referred to in the industry as a bleed out condition which may result in molten metal escaping into the casting area and casting pit.
While in some prior art the molten metal surface level sensor has been moved to a location to sense metal outside of the oxide barrier or dam, this is not as desirable for multiple reasons, such as incomplete oxide retention, and especially in certain applications.
It is therefore desirable and an object of this invention to more effectively and accurately control the level of molten metal in continuous cast molds by controlling, managing and routing the oxides forming on the surface of the molten metal, while maintaining sufficiently accurate molten metal surface area sensing and monitoring.
It is therefore an object of some embodiments of this invention to provide a system for more effectively and accurately controlling the level of molten metal in continuous cast molds by controlling, managing and routing the oxides forming on the surface of the molten metal.
Other objects, features, and advantages of this invention will appear from the specification, claims, and accompanying drawings which form a part hereof. In carrying out the objects of this invention, it is to be understood that its essential features are susceptible to change in design and structural arrangement, arrangement with only one practical and preferred embodiment being illustrated in the accompanying drawings, as required.